The present invention relates to improvements in vapor recovery fuel dispensers, particularly those with positively driven vapor pumps.
Vapor recovery fuel dispensers, particularly gasoline dispensers, have been known for quite some time, and have been mandatory in California since the early 1980's. The primary purpose of using a vapor recovery fuel dispenser is to retrieve or recover the vapors which would otherwise by emitted to the atmosphere during a fueling operation, particularly for motor vehicles. The vapors of concern are generally those which fill the vehicle gas tank. As the liquid gasoline is pumped into the tank, the vapor is displaced and forced out through the filler pipe.
The traditional vapor recovery apparatus is known as the "balance" system, in which a sheath or boot encircles the liquid fueling nozzle and connects with tubing back to the fuel reservoir. As the liquid enters the tank, the vapor is forced into the sheath and back toward the fuel reservoir where the vapors can be stored or recondensed.
Balance systems have numerous drawbacks, including cumbersomeness, difficulty of use, ineffectiveness when seals are poorly made, and slowed fueling rates.
As a dramatic step to improve on the balance systems, Glibarco, Inc., assignee of the present invention, patented an improved vapor recovery system for fuel dispensers, U.S. Pat. No. 5,040,577 to Kenneth L. Pope. The Pope patent discloses a vapor recovery apparatus in which a vapor pump is introduced in the vapor return line, driven by a motor. The liquid pump includes a pulser, conventionally used for generating pulses indicative of the amount of liquid fuel being pumped. A microprocessor translates the pulses indicative of the liquid flow rate into a desired vapor pump operating rate. The effect was to permit the vapor to be pumped at a rate correlated with the liquid flow rate so that, as liquid is pumped faster, vapor is also pumped faster, and vice versa.
While the apparatus described in the Pope patent is significant and quite workable, various improvements and refinements have been discovered to further enhance the usability of it and similar vapor recovery systems.
In particular, since the vapor pump is independently driven, in the event of a malfunction so that the vapor pump is operating when the liquid pump is not, there is a possibility of drawing large volumes of air into the liquid storage tank. When the quantity of air reaches a high enough level, the air/vapor mixture in the tank can reach dangerously explosive proportions. Accordingly, safety features are needed to assure that excessive amounts of air are not drawn in.
In addition, some liquid fuel dispensers have multiple pumps, drawing from different fuel reservoirs, so different grades of fuel can be combined to make a blended product. The Pope patent does not address how to control the vapor pump in such a circumstance.
Further, it has been found that if liquid is pumped back through the vapor pump line, damage to the vapor pump can result, so that a need is present to deal with that circumstance.
Also, a need still existing is to prevent the escape of the vapor from the vapor pump recovery system during periods of idleness. Accordingly, these and other needs still remain unfulfilled.